In order to precisely move and control the positioning of a carriage within a precision apparatus such as a high data density tape recorder, a lead screw drive may be incorporated into the carriage of an actuator for the tape drive or similar high precision device.
The carriage is positionable by operation of the lead screw drive to displace a magnetic head to the nominal position of a data track on a magnetic tape to be recorded or read. Finer positioning of the magnetic read/write head may be controlled by a voice coil motor (VCM) driving the read/write head in small dynamically controlled positioning moves. The more precise the positioning of the carriage relative to the magnetic tape and the magnetic head relative to the carriage and, thus, relative to the magnetic tape, the less demand is placed on the voice coil motor drive to precisely drive and position the head relative to the track to be recorded or read.
Due to the nature of lead screw drives, the lead screw axis must be confined to a fixed spatial position relative to the carriage and the actuator of the tape drive. Any lack of fixed positioning of the lead screw axis further burdens the VCM and VCM driven components to compensate for the imprecision on a dynamic basis for servo applications as well as degrading head positioning in tape drives without VCM compensation apparatus. The need to position the lead screw axis relative to the carriage is primarily one of consistency inasmuch as the VCM can make compensatory adjustments to ultimately position the magnetic head.
The spacial consistency of the axis location must be addressed in order to maintain a high level of consistency for the magnetic head positions relative to the magnetic tape and its recording tracks. The location of the lead screw axis may be defined and that definition refined by eliminating any play or tolerance clearances which may permit or induce movement of the lead screw relative to the bearing which constrains the lead screw. Bearings designed and built with very tight tolerances and dimensions will result in a zero or at least a low clearance bearing but in the process may very well result in excessive frictional loads and typically are of relatively high cost.
Due to the small size of the drive components in a typical high density data tape drive, it is most desirable to minimize the loading and particularly the frictional loading on the drives that position the head.
The compact design of very high data density tape drives leaves very little room for components; thus, although designed to provide low frictional resistance and precise location of the axis of any lead screw associated therewith, precision linear bearings are typically too large for inclusion into such designs. Additionally, such conventional precision bearings are extremely expensive and accordingly are not practical for inclusion into a mass produced design, such as that found in high density tape drives.
Bearings of sufficiently small size having the necessary precision have been similarly much too expensive and thus not prime candidates for selection as included components.
In tape drives particularly high density data tape drives, the orientation referred to as the azimuth angle between the magnetic head and the magnetic tape is tightly controlled in order to insure the ability to write and then read the data correctly from the magnetic tape. In order to maintain a constant azimuth angle, it is necessary to eliminate any undesirable and unwanted relative movement of the carriage and the magnetic head relative to the magnetic tape.